Chromoly vs. Mild steel cage

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by BLOWN347STROKER, Jun 28, 2010.


  1. BLOWN347STROKER

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    Ok over the weekend I have been doing some thinking. I have already ordered a 10 pt cage for my 94 cobra project that meets NHRA Guidelines for a mild steel cage. I have had some people tell me that I should have gone chromoly. I went with mild steel because it was obviously cheaper and I have no access to a tig welder where as I have a mig welder sitting in my garage so I can install it myself. This is not just a strip car. In fact it will be a mostly street car with a track run every now and again. The quesion is did I make a mistake. Should I have gone chromoly or do you guys think I will be ok with mild steel. Here are NHRA guidelines.

    How do I get Blueprint Specifications or Classification Guide information?
    Classification Guides and Engine Blueprint Specifications are now available for free download. Click here for [Classification Guides] or here for [Engine Blueprint].

    Do I need a helmet, and if so, what kind?
    A helmet is required for the driver of any car or truck running 13.99 seconds or quicker in the quarter mile, and for the rider of any motorcycle. Most drivers can use a helmet meeting SNELL K98, M2000, SA2000, M2005, or SA2005 specifications. Professional category and some alcohol burning vehicles require an SA rated helmet. It is important to note that the helmet rating must be designated on a tag INSIDE the helmet, or sewn to one of the helmet straps. The designation stenciled on the exterior of the helmet is insufficient for NHRA technical inspection. Also, some tracks require a helmet on ALL drivers, so check in advance.

    When do I need a roll bar or roll cage, and what should it look like?
    A roll bar is required in any convertible running 13.49 seconds or quicker in the quarter mile, and in other cars beginning at 11.49. The roll bar is accepted in vehicles running as quick as 10.00 second e.t., provided the stock firewall and floorboard is intact, other than for installation of wheel tubs. The rollbar must be constructed of minimum 1 ¾ inch o.d. x .118 inch wall mild steel tubing, or 1 ¾ x .083 chrome moly tubing, and must conform to the following diagram:



    If the floor and/or firewall has been modified, then a full roll cage is required beginning at a 10.99 e.t. A full roll cage is required in any vehicle running 9.99 seconds or quicker, and any vehicle running 135 mph or faster (regardless of e.t.). The roll cage must be constructed of minimum 1 5/8 o.d.x .118 mild steel tubing, or 1 5/8 x .083 chrome moly tubing, and must conform to the following diagram:

    The roll cage of any vehicle running 9.99 or quicker, or 135 mph or faster, must also be certified by NHRA every 3 years, and have a serialized sticker affixed prior to participation.

    How, where and when do I get a roll cage certified?
    Contact your Division Office (click here for contact info) and tell them you need a chassis certified. They will direct you to the NHRA Chassis Inspector in your area. Chassis certifications are also performed at all National and Divisional events, for participants. Due to busy event schedules, certifications are not always available at events for non-participants. Contact the Division office (for Division events) or the National Technical Department in Glendora (for national events) ahead of time to see if arrangements can be made. Three year certification stickers (for vehicles running 7.50 seconds and slower) are $150. If you arrange for a chassis inspector to come to your location, you will be responsible for any travel expenses.

    I have a street car that I occasionally run at the strip. I've relocated the battery to the rear. What else do I need?
    Any car with a relocated battery must be equipped with a master electrical cutoff, capable of stopping all electrical functions including ignition (must shut the engine off, as well as fuel pumps, etc.). The switch must be located on the rear of the vehicle, with the "off" position clearly marked. If the switch is of a "push / pull" type, then "push" must be the motion that shuts off the switch, and plastic or "keyed" typed switches are prohibited. Also, the battery must be completely sealed from the driver and/or driver compartment. This means a metal bulkhead must separate the trunk from the driver compartment, or the battery must be located in a sealed, metal box constructed of minimum .024 inch steel or .032 inch aluminum, or in an NHRA accepted plastic box. In cars with a conventional trunk, metal can simply be installed behind the rear seat and under the package tray to effectively seal the battery off from the driver. In a hatchback type vehicle the battery box is usually the easiest solution, since the alternative is to fabricate a bulkhead which seals to the hatch when closed. At present, Moroso is the only company which offers an NHRA accepted plastic battery box, part number 74050.

    But I drive on the street. I don't want a big cut off switch hanging on the back.
    This solution takes a little work, but it solves the problem. Install the master cutoff inside the vehicle, positioned "sideways" so that the toggle moves forward and back. Drill a hole in the toggle handle, and attach a steel rod that will run out the back of the car, through a hole drilled completely through one tail light assembly. Have a spare tail light assembly on hand, so when you come home from the drags, you remove the rod and put the cherry tail light back in for street cruising. Next time you plan on going to the drag strip, swap lights and reinstall the rod. Since the drilled light is for the strip only, you can also have it marked "PUSH OFF" in big letters so the Tech Inspectors will think you're cool.

    What is "SFI"?
    The SFI Foundation, Inc. is an independent company that writes minimum specifications for various pieces of equipment used in all types of motorsports. When a manufacturer affixes a "Meets SFI Specifications" tag to a product, the consumer, as well as the sanctioning body, is assured that the product is made to some minimum standard. Without the tag, it is up to the consumer and/or technical inspector to make a decision as to the level of quality in a particular product. Most SFI specifications are performance oriented, in that they define what type of testing a product must be able to withstand before failure.

    How do I obtain a copy of SFI chassis specifications?
    These must be purchased directly from SFI. SFI can be reached by phone at 858-451-8868. Most of the specs now contain color coded illustrations, and are helpful to anyone building a chassis, even if the vehicle will not reach a performance level requiring an SFI spec chassis.
     
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  2. 90lxcoupe

    90lxcoupe Mustang Master

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    you will be ok with moly and like you said, you can MIG it yourself so thats going to save you some money. Moly is just lighter then mild steel. FWIW NASCAR uses all mild steel in the cars they build
     
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  3. BLOWN347STROKER

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    Ok i think you have it confused. I got a mild steel cage and can mig weld it. Chromoly would require tig welding. From what I can tell though the cage I ordered still meets the requirements though.
     
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  4. 90lxcoupe

    90lxcoupe Mustang Master

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    yea i meant to say mild steel, just a typo. Mild steel will be 100% legal to 8.50, and i am not 100% sure but i think cars 7.50 and faster are required to have a moly cage. I read a big argument on the bullet on how mild steel is actually stronger then chromoly
     
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  5. Cobra912

    Cobra912 Active Member

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    dude your fine with the mild. I just got my mild steel shipped in and other than weight savings there is no big difference. And of course price which is why I went that way. Stick with what you ordered and do it yourself
     
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  6. Bills89GT

    Bills89GT New Member

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    I wish I had asked this same question. I did it the other way around. I have a 8pt chromoly cage from S&W race cars. I didn't realize till I got it and read the directions that it needed to be tig welded. I said the hell with it and mig welded it. They sent me a wrong piece so I had an extra one to play around with and the pipe bends before the weld breaks so I think i'm good... Besides my car will never be fast enough to have to worry about even needing a cage

    That chromoly is tough stuff though! I am an electrician and run a lot of galvanized rigid metal conduit at work and use an electric bender. Our bender had a hell of a time bending that stuff and it's a much thinner wall than our conduit. And if anyone out there plans on cutting it with a hand held band saw, buy some good blades.. and a lot of them!

    Good luck with the cage though!
     
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